There is the story of this sailor who experienced a terrible shipwreck at sea. He climbed upon a raft and set his course based on the stars since he has learnt to navigate from the stars.
Yet for the next 28 days, the clouds cover the sky every night and he is uncertain whether he remains on course or whether he is doomed.
The question is had the sailor set his course right? The message of the constellations - had he imagined it because of his desperate circumstances? Or he had seen the truth once, and now had to hold on to it without further reassurance?